The present disclosure relates to a GaN-based semiconductor light-emitting element, a light-emitting element assembly and light-emitting apparatus including the GaN-based semiconductor light-emitting element, a method of driving the GaN-based semiconductor light-emitting element, and an image display apparatus including the GaN-based semiconductor light-emitting element.
In a light-emitting element (GaN-based semiconductor light-emitting element) including an active layer composed of a gallium nitride (GaN)-based compound semiconductor, a light emission wavelength in a wide range from ultraviolet to infrared can be realized by controlling the band-gap energy by changing the mixed crystal composition or thickness of the active layer. GaN-based semiconductor light-emitting elements that emit various types of colors are commercially available and used in various applications such as an image display apparatus, a lighting device, a test apparatus, and a light source for sterilization. Furthermore, semiconductor lasers and light-emitting diodes (LEDs) that emit blue-violet light have also been developed and used as pickups for writing or reading of large-capacity optical discs.
In general, a GaN-based semiconductor light-emitting element has a structure in which a first GaN-based compound semiconductor layer of n-conductivity type, an active layer, and a second GaN-based compound semiconductor layer of p-conductivity type are sequentially laminated.
In such a GaN-based semiconductor light-emitting element, in order to realize a high luminous efficiency, various techniques related to an active layer composed of well layers and barrier layers have been proposed. Examples of the techniques in the related art include a technique in which the number of well layers is specified (for example, see Japanese Unexamined Patent Application Publication Nos. 10-261838 and 10-256657), a technique in which the mixed crystal compositions of well layers and barrier layers are specified (for example, see Japanese Unexamined Patent Application Publication Nos. 2000-261106 and 2000-091629), and a technique in which a multi-quantum barrier structure is provided to barrier layers disposed between well layers having different light emission wavelengths, thereby controlling the emission intensity ratio of a plurality of light emission peaks (for example, see Japanese Unexamined Patent Application Publication No. 2002-368268). Note that in the multi-quantum well structures disclosed in these patent applications, it is assumed that all the barrier layers have the same composition, the same thickness, and the same structure. Japanese Unexamined Patent Application Publication No. 2004-179428 discloses a technique in which the composition of each of barrier layers is varied. This patent application describes that holes and electrons can be intentionally concentrated on a well layer located close to a p-side cladding layer. Furthermore, Japanese Unexamined Patent Application Publication No. 2004-087763 discloses a technique in which a strain-compensating layer is formed between a well layer and a barrier layer.
In any technique disclosed in the above-mentioned patent applications, when the density of current applied to an active layer is increased, it is difficult to prevent the luminous efficiency in the active layer having a multi-quantum well structure from decreasing. Accordingly, a technique for realizing a higher luminous efficiency has been strongly desired.